NTN Received “Best Paper Award” and “Tribo-Technology Award” of Japanese Society of Tribologists 2021

NTN Corporation (hereafter, NTN) received “Best Paper Award” and “Technology Award” of Japanese Society of Tribologists*1 2021. The theme is “Estimation Method of Micropitting*2 Life from S-N Curve Established by Residual Stress Measurements and Numerical Contact Analysis(Best Paper Award)” and “Low Friction Technology for Sealed Rolling Bearings for Transmissions(Tribo-Technology Award)” We received these awards in recognition of the novelty, originality, and contribution to industry in research and technology.

Society that promotes the academy and scientific technologies related to tribology, and contributes to theoretical advances and technological improvements related to tribology.

Tiny surface spalls due to rolling contact fatigue at asperity contact points(In the paper, it is called “micropitting”)

1. About “Best Paper Award of Japanese Society of Tribologists 2021”

Proposed highly accurate bearing operating life estimation method which can provide optimum bearing specifications for operating conditions that are becoming more severe every year.

Name of winner

Naoya Hasegawa, Supervisor, Advanced R&D Center of NTN
Takumi Fujita, Manager of Product & Business Strategic Planning Dept. of NTN
Michimasa Uchidate, Professor of Faculty of Science and Engineering, Iwate University
Hiroshi Kinoshita, Professor, Masayoshi Abo, Associate Professor of Graduate School of Engineering, University of Hyogo    

Awarded theme

Estimation Method of Micropitting Life from S-N Curve Established by Residual Stress Measurements and Numerical Contact Analysis    

In order to achieve carbon neutrality, there is increasing demand to reduce environmental impacts. Thus, technology development of machinery for electrification, downsizing, lightweight, and low friction is promoted. For example, electric motors in automobiles tend to become smaller and faster. Beside these trends there is a need to consider the reduction of lubricant viscosity in order to suppress heat generation and energy loss, which are caused by the stirring resistance of lubricants. In addition, oil pumps used as accessories in electric motor transmissions are also being downsized, and further reduction of lubricant viscosity is being considered to reduce the burden on the pump. The reduction of lubricant viscosity makes the lubrication conditions of rolling bearings more severe. NTN has responded to this market trend by taking the lead in the research on accurate operating life estimation of rolling bearings used in severe lubrication conditions.

The reduction of lubricant viscosity is a factor that reduces the oil film thickness of rolling bearings in operation and advocates to occur the micropitting on the contact surfaces of rolling bearings. The micropitting life is shorter than the life under sufficient oil film formation, and it has been difficult to accurately estimate the micropitting life.

Our method can estimate the micropitting life more accurately than conventional methods because of following two reasons. First, our method is based on the mechanism of micropitting that have clarified through joint research with universities. Second, while conventional methods consider changes in residual stresses and surface roughness only on the basis of theory, our method consider them by measurement such as rolling tests. Therefore, our method can estimate the micropitting life more reliable than conventional methods.

Reasons for award

The proposed method can be used to design the surface roughness of rolling bearings to prevent micropitting and to determine the need for surface treatment. Also, it can also be used to determine appropriate bearing specifications while ensuring its reliability and manufacturing cost. In addition, It can be useful in determining whether it is possible to use low viscosity oil, the need for additives to lubricating oil, and the compatibility of reliability and low friction in rolling bearings. Furthermore, this technology can estimate the remaining operating life of bearings by measuring the surface roughness and residual stress of rolling bearings in use, thereby contributing to the stable operation of customers' facilities through appropriate maintenance. The award was given to this research not only for its novelty and originality, but also for its contribution to the development of industry.

2. About “Tribo-Technology Award of Japanese Society of Tribologists 2021”

Achieves both low torque and long operating life for automotive bearings. Contributes to the development of EVs, HEVs, etc. by supporting high speed rotation.

Name of winner

Tomohiro Sugai, Supervisor, Advanced R&D Center of NTN
Katsuaki Sasaki, Supervisor and Takahiro Wakuda, Supervisor of Automotive Bearing Engineering Dept., Automotive Business HQ. of NTN    

Awarded theme

Low Friction Technology for Sealed Rolling Bearings for Transmissions    

As automobiles become more fuel efficient, bearings for transmission are required to have not only longer operating life but also lower friction. In addition, in order to prevent the life of bearings decreased due to gear wear debris in the lubricating oil, contact type seals have been used to prevent the intrusion of foreign matter, but the contact of the seal with the inner ring of bearing increases rotational torque.

In order to meet market needs for longer operating life, lower friction, and higher speeds, NTN has developed a new contact type seal with arc-shaped micro convexes at equal intervals on the sliding surface of the bearing contact seal. It reduces rotational torque by 80% compared to conventional products. The developed product has succeeded in significantly reducing rise in temperature compared to conventional products even under high rotational speed conditions by achieving a rotational torque equivalent to that of a non-contact seal while it is a contact-type seal. In addition, the projection height, a key point of development, is extremely small and intercepts foreign matter that decrease the life, thus ensuring bearing operating life equivalent to that in an environment with no foreign matter, and achieving both low torque and high reliability.

Reasons for award

This technology significantly reduces the rotational torque of bearings for transmission compared to conventional products, contributing to fuel efficiency of automobiles. It also achieves a longer operating life of more than five times longer than that of conventional products under foreign object lubrication It also contributes to downsize of the bearing and, consequently, to reduce the weight of automobiles. Furthermore, the bearing can operate at more than twice the rotational speed of conventional contact type seal bearings. This enables the bearing to accommodate the higher speeds required by the shift to electric vehicles. These points have been highly evaluated and won the Technology Award.